A study investigated how elementary school students form a mental representation of simple addition and subtraction word problems, focusing on critical elements in the problems' semantic structure, and the extent to which the accuracy of the solutions found was related to the students' English language proficiency when the problems were presented in both Spanish and English. Subjects were 119 Mexican-American students in grades 2-5, divided into high (n=72 students) and low (n=47) English proficiency groups. Students were asked to solve 14 problems and answer 4-7 probe questions for each problem, designed to assess knowledge of information needed to solve the problems. Results show a main effect for grade level and language proficiency, and an interaction effect between grade level and proficiency. No difference was found between low and high proficiency students in accuracy of solutions, but low-proficiency students in higher grades performed less well on problems presented in both English and Spanish, contrary to expectation. Students who were able to answer comprehension questions generally got accurate solutions, although younger students had inadequate underlying semantic conceptual representation of the problem to find an accurate solution. Specific factors were associated with accurate comprehension. Problems and statistical results are appended. (Contains 27 references.) (MSE)